In recent years, low density parity check (LDPC: Low Density Parity Check) code is becoming popular as error correction code that makes the most of high error correction performance on a feasible circuit scale. The LDPC code is an error correction code defined by a low density parity check matrix H. “Low density” means that the number of “1” elements included in a matrix is considerably smaller than the number of “0” elements. The LDPC code is a block code having the same block length as the number of columns N of parity check matrix H.
Because of its high level error correction performance and ease of mounting, the LDPC code is adopted for a high-speed wireless LAN (Local Area Network) system of IEEE802.11n and an error correction coding scheme such as a digital broadcasting system. Furthermore, an adoption of QC (Quasi Cyclic)-LDPC code on a home network is also under study.
The block code has a feature that the error correction performance improves as the block code length increases. When, for example, symbols such as a header for transmitting control information or the like are wished to be transmitted reliably, receiving quality of the header can be secured using a block code longer than the header.
Furthermore, using the same error correction code as the error correction code used to transmit information and the error correction code used to transmit the header is advantageous from the perspective of the circuit scale. The present application refers to and describes a symbol for transmitting control information or the like as “header,” but a symbol for transmitting control information or the like may also be referred to as “control symbol (control channel or control signal),” “preamble,” “tail symbol,” “pilot symbol (pilot channel or pilot signal),” “training symbol” or the like.
In this case, as shown in FIG. 1, when the number of information bits that need to be transmitted (e.g., header length) is less than the block length of the block code, parity bits are generated by performing coding assuming that information bits in the excess part of the block length are 0's.
As a coded sequence to be actually transmitted, only information bits that need to be transmitted (e.g., header) and parity bits are transmitted as shown, for example, in FIG. 1. That is, the portion of information bits assumed to be 0's is not actually transmitted.
A header of control information, for example, generally has a smaller number of bits than payload data that transmits information such as an image. However, by transmitting the header and parity bits as shown in FIG. 1, the header and payload data can be encoded using the same block code. Furthermore, since the header is encoded using the block code of a greater block length than the header length, receiving quality of the header can be secured. As a result, since the header can be reliably transmitted to the communicating party, the aforementioned communication method is effective in establishing communication.